Patent GB-932400-A (GB)
Title: Electromagnetic system for the maintenance of the movement of a rotating member such as a balance of a timepiece
IPC: G04C3/06
Filed: 1960-07-11
Abstract: 932,400. Clocks and watches. FABRIQUES NOVADO. July 11, 1960 [July 11, 1959 (2)], No. 24074/60. Class 139. An electromagnetic arrangement for driving a timepiece balance or like rotary member includes at least one rotary element coupled to the balance or like member and made of magnetizable material of very low remanence, at least one electrical drive winding arranged to apply periodic drive impulses to the said element or elements, an electrical circuit including means for supplying to the drive winding current pulses which generate the drive impulses, and an electrical capacitance which is periodically charged and is discharged through the drive winding after and in the opposite direction to each current pulse, so as to destroy any magnetization remaining in the rotary element. In the first example, Figs. 1 and 2, an E-shaped permanent magnet 10 inside a screen 15 cooperates with two interconnected blades 11 made of low remanence magnetizable material and mounted on the balance staff 12 encircled by a stationary winding 14 including pick-up and driving coils. The maintaining circuit includes a capacitor which is charged and then discharged into the driving coil to destroy any residual magnetism in the blades. Two diametrically opposed magnets may be provided. In another example. Figs. 4 and 5, two pairs of permanent magnets 19 are carried by plates 17 fixed to the balance staff 18, and are screened by tubes 20. The plates 17 and tubes 20 are made of a material having high magnetic permeability and low remanence. The magnets co-operate with the heads 21 of a V- shaped stationary magnetizable member 16 carrying the Bc Bm. In another example, only one or two magnets are provided and the heads of the member or each member 16 are superimposed. In the maintaining circuit the drive coil may be connected to the collector or emitter of a transistor and the pick-up coil to the emitter or base. In one example, Fig. 9, a capacitor C is connected across the drive coil Bm and a thermistor R is connected to the base of the transistor and to the pick-up coil Bc. The capacitor C may be connected in series with the driving coil. The resistance R allows locking of the transistor after each driving impulse and an additional capacitor may be provided for the purpose. A diode may be connected to bias the transistor base. Further circuits providing temperature compensation are described, one including a thermistor and a Zener diode, one including a driving coil subdivided into two parts and one including a second transistor. In the embodiment shown in Fig. 19, the member 11 carried by the balance staff co-operates with the coil carrying cores 13, 14 extending from a stationary section 10 of magnetizable material of low remanence. The section 10 includes a cylindrical screen 12. The non-diametrically opposed location of the cores 13, 14 and extensions 17, 18 of the member 11 result in impulsing in one direction only. The extensions 17, 18 may be toothed. In another example the coils are wound on a V- shaped member as in Fig. 4 and the cylindrical screen is gapped. The V-shaped member may have upstanding lugs between which the rotor oscillates. The coil carrying member may be U-shaped, Fig. 23, to co-operate with heads 25, 26 extending from a ring 27, the heads being of different sizes to ensure impulsing in one direction only. The coil carrying member may be of circular or square shape. The rotor may be made from a shaped cut plate.